A Farmer Decides She Wants to Grow Certified Organic Corn

A farmer decides she wants to grow certified organic corn and sets out to meet all USDA standards to do so. Her crop grows well for the first 3 years; however, she notices during the 4th and 5th years that plants are getting smaller and producing much less corn. She has not altered farming practices and begins to wonder what is happening. She remembers someone mentioning planting peanuts every 3rd year in place of a corn crop, which leads to much healthier corn. Why would a farmer want to change to a different crop, especially something like peanuts?

A) Planting a legume like peanuts increases water retention in the soil, allowing the following year's corn crop to thrive.
B) Crop rotation with a legume like peanuts will increase nitrogen in the soil, reducing the need for chemical fertilizer.
C) Planting a legume like peanuts increases the available carbon in the soil.
D) Changing from corn to peanuts, a legume, allows the soil to "rest" for a year.